WRECKTOUR:155 The Gretafield

THIS MONTH WE ARE ALMOST as far north on the UK mainland as you can get, to tour the wreck of the 10,191-ton tanker Gretafield.
The Gretafield was torpedoed and caught fire in 1940, then, abandoned and ablaze, drifted into Dunbeath Bay.
The combination of fire damage and 61 years of winter storms and shallow water means that the wreck is well broken up, but there is still plenty to see.
From the early days of steamships, tankers almost universally had their engines at the stern, thus keeping the fire and heat of the boilers and any sparks from the funnel away from the flammable cargo of oil.
As a consequence, our tour of the Gretafield begins as it often does on the boilers, but at the stern of the ship.
The Caithness Diving Club members with whom I was diving dropped the shot on the forward starboard boiler (1), the first of six boilers that provided steam to the Gretafield’s huge engine.
This boiler has somehow rolled out of the hull beyond 180° from its normal orientation, as evidenced by the three fire-boxes at the back of it now being upside-down. What is surprising is that to get to where it is resting, it must also have jumped over a large section of hull that still stands just inside it.
I suspect that by the time the superstructure of the burning wreck broke up, the boiler was empty of water and consequently floated out, but then rolled over, dumping the air trapped inside to sink upside-down and outside of the hull.
Heading aft, the next boiler (2) has been through a similar sequence of events, though this time tipping on end to dump trapped air and sink with the fire-boxes now pointing to the surface, reaching as shallow as 5m.
Immediately after this boiler are two cylinders of the steam engine (3), fallen to starboard and over the broken edge of the hull. One of these has broken apart to leave the piston exposed and the crown of the cylinder tipped against the back of the boiler.
Staying outside the hull for now, right at the stern the propeller-shaft and stern gland (4) protrude above the 12m seabed, showing just how far the hull of the Gretafield has broken down. On a wreck this shallow and accessible, the prop was likely salvaged soon after the sinking.
Just off the stern, a curved plate that is partly buried in stones and gravel could have been the rudder (5).
From the stern gland, a short section of propeller-shaft (6) leads forward to the crankshaft, breaking where the body of a turbine has been removed, though part of the turbine (7) remains at the back of the engine.
The purpose of the turbine would have been to extract the last bit of power out of the steam after it came out of the low-pressure cylinders of the engine.
I say cylinders, because two more (8) have fallen to port, making a total of four.
Looking at the relative size of the cylinders, the Gretafield’s engine would still have been triple-expansion, but with the low-pressure stage being split between two cylinders.
The six boilers of the Gretafield were arranged in two rows of three across the hull. Like the first two, the middle boiler of the back row (9) has floated out of its mount and, like the second boiler, stands on end with the fire-boxes uppermost.
The final boiler of the back row (10) has rolled out of the port side of the hull, but is only 90° over.
On the forward row, the middle boiler (11) has shifted to starboard, but has somehow contrived to roll 90° to port.
Finally, the port forward boiler (12) stands on end and a little forward, still inside the hull.
Forward of the boilers, an entire bulkhead (13) has collapsed across the wreck. This marks the end of the machinery.
As a tanker, the forward part of the hull would have been just a massive grid of oil and ballast tanks, with pipework on the deck above, now smashed almost level with the seabed. However, there are still some notable bits of wreckage and, at only 12m deep, plenty of bottom time should be available to have a look.
Further forward towards the centre-line, a mast (14) has fallen backwards inside the wreck.
Just forward of this, a massive box-section (15) spans the width of the hull. Perhaps this was part of the foundation for the mast.
Hull-plates have fallen outward on both sides of the wreck.
To the starboard side, close to the box-section, is a large rectangular compartment (16). It looks to have landed upside-down from above the deck – perhaps part of the superstructure and wheelhouse amidships.
Forward of the box-section are a pair of bollards and then a plate with a line of empty holes from portholes (17), also from the amidships superstructure.
Further forward, the wreckage is again
a devastated confusion of steel plates (18). As the wreck begins to fizzle out, off
to port is a tubular framework (19). This could have been part of a mast, or perhaps it was fitted beneath the bow to tow mine-sweeping cables and paravanes.
Members of the Caithness Diving Club tell me that there are some anchors and bits of winch-gear and bollards right in the shallows among the rocks and kelp, but it is too kelped and shallow to be worth continuing further inshore.
Our route consequently returns to the stern, most easily by following along the starboard side of the hull (20), to where a tall section of hull (21) rises by the boiler where we started.
There should be no trouble relocating the shotline, but in water this shallow it is just as easy to make a safety stop sitting on top of one of the boilers before blobbing to the surface.

Thanks to Davy Carter, Mark Liddiard, Ian Mackay, Caithness Diving Club, Tony Jay, Victoria Bennett, Tim Walsh and Rachel Locklin.

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